Recently, polymer materials have been desired which have high heat resistance, high tenacity in extreme conditions such as in cosmic space, and easy moldability. Patent Literature 1 describes a method of attaining high heat resistance in molding without generating volatile components by heat curing while maintaining good processability wherein a polyimide oligomer is heated and capped with a capping agent such as phenylethynylphthalic anhydride, molded, heated and, then, crosslinked and cured at the phenylethynyl group. Patent Literature 2 discloses a method for improving flowability and processability of an oligomer using asymmetric tetracarboxylic anhydride in the preparation of a composite of carbon fiber and polyimide. A cardo-type diamine is used in Patent Literature 3. The asymmetric diamine disclosed in Patent Literature 4 is 2-(4-aminophenoxy)-5-aminobiphenyl.
In particular, 2-(4-aminophenoxy)-5-aminobiphenyl described in Patent Literature 4 is a raw material for preparing a polymer having high heat resistance, high tenacity and easy moldability and broadens the potentiality of asymmetric polyimides (Non-Patent Literature 1). Non-Patent Literature 2 describes that many of asymmetric polyimides have a high melt flowability on account of active segmental movement at a temperature higher than a glass-transition temperature. Therefore, further asymmetric diamines are desired to be used as a raw material of asymmetric polyimides.